1. Field of the Invention
This invention relates to fireplaces, and more particularly, to a metal (steel) fireplace which is insertable into an existing masonry fireplace and compatible with the existing chimney or flue structure of the masonry fireplace and which substantially increases the efficiency of the utilization of heat produced by the fireplace.
2. Description of the Prior Art
As is well known and understod, fireplaces have existed in various forms for many years, even for perhaps thousands of years. As is also well known and understood, fireplaces are relatively inefficient in the utilization of heat produced by the burning or combustion of fuel in the fireplaces. Various suggestions have been made toward increasing the efficiency of fireplaces, such as the well known "heatolator" type fireplace, in which a metal (steel) fireplace is used with double walls on the sides of the firebox or combustion chamber, and, by convection, air is drawn in at the bottom of the sides, heated, and moves outwardly at the upper portion of the fireplace sides.
Even more recently, particularly associated with the energy conservation movement of recent years, attempts have been made to increase further the efficiency of fireplaces.
U.S. Pat. No. 462,197 illustrates the use of tubes or pipes which extend across, in a generally vertical manner, a fireplace combustion chamber for heating air flowing by convection in the pipes. The pipes communicate with a cold air chamber at their lower end, and with a hot air chamber at their upper end.
U.S. Pat. No. 929,436 discloses a heater in which pipes are used for heating water. A double walled structure is disposed about the combustion chamber for increasing the efficiency of the heat utilization.
U.S. Pat. No. 2,258,882 and U.S. Pat. No. 2,322,016 both disclose double wall apparatus in which convection currents are utilized to increase the efficiency of the heat produced from combustion by using a fireplace to heat auxiliary air moving around the fireplace apparatus.
U.S. Pat. No. 2,453,954 discloses a stove insertable in a fireplace. Hollow tubular grates are used. The hollow grates pick up air at the rear of the fireplace, and allow the heated air to flow outwardly through the front of the fireplace.
U.S. Pat. No. 2,470,430 discloses a fireplace in which outside air is brought into a fireplace by a system of ducts.
U.S. Pat. No. 2,789,554 also discloses the use of an auxiliary air flow to increase the efficiency of the fireplace, by inserting ductwork around the fireplace and above the fireplace in the chimney flue area.
U.S. Pat. No. 3,845,754 discloses separate air flow systems, one for combustion air and a second for heated air.
U.S. Pat. No. 3,926,175 discloses a metal fireplace which utilizes outside air for combustion air and also for heating. The incoming outside air mixes with air within the structure, and the two air systems are not separated for heating or combustion purposes.
U.S. Pat. No. 3,976,048 discloses fireplace apparatus which includes two separate air systems, one for combustion purposes, which is outside air, and a second for heating purposes. The combustion air is ducted to the front of the combustion chamber.
U.S. Pat. No. 4,026,263 discloses fireplace apparatus in which two air systems are utilized, outside air for combustion, and the outside air also mixes with the inside air for the circulation of heated air. Hollow grates are also used to increase the efficiency of the apparatus. The front of the combustion chamber of the fireplace is also sealed, as with the '048 apparatus.
U.S. Pat. No. 4,059,090 discloses apparatus which includes a housing surrounding a firebox and the housing is vented to outside air and also to the interior of the structure in which the apparatus is disposed. Exterior air is drawn into the housing, it is circulated about the firebox, and through conduits which extend through the chimney flue before exhausted into the room or structure through a front vent. A portion of the same flow of air is also passed through the bottom of the unit to provide air for combustion. Additionally, air from within the structure or house flows through the front doors of the apparatus to provide additional air for combustion purposes.
A plurality of conduits extend across the flue in the '090 patent for providing additional heating of the air passing through them. It will be noted that this feature, the provision of ducts extending through the flue, is also disclosed in the '236 patent and the '048 patent, discussed above, and in the '488 patent, discussed below.
U.S. Pat. No. 4,061,127 discloses a fireplace disposed in a mobile home, with the conbustion chamber sealed and outside air used for combustion purposes. Doors at the front of the fireplace are used to seal the combustion chamber from the interior of the mobile home.
One of the most efficient prior art fireplaces is disclosed in U.S. Pat. No. 4,135,488. Two separate air flow systems are used in the '488 apparatus. One air system is for combustion air, drawn from outside the home or structure in which the fireplace is disposed. A second air flow system uses inside air, circulated about the apparatus, and into the home or structure after being heated.
In addition to the above cited patents, there are hollow tubular grates which curve upwardly and forwardly. The lower portion of such structure comprises a relatively horizontally extending grate structure on which fuel is disposed for burning. Air is drawn into the lower portion of the grates and is heated as it flows through the grates. The heated air is then returned to the room.
One of the problems of such apparatus is burning. The heat radiates outwardly and downwardly from the lower portion of the hollow grates and reflects back, burning the grates. The burnout of such apparatus accordingly results in a relatively short period of time.